JPH1059203A - Control unit of motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a required memory capacity and to smoothly change a steering subsidiary command value by calculating a steering subsidiary command value corresponding to a steering torque on the basis of a prescribed functional expression. SOLUTION: A desired steering subsidiary command value corresponding to a steering torque can be represented by a high order functional expression having a characteristic curve (a). In this case, four points p, q, r and s satisfy the high order functional expression. One approximate expression having a characteristic curve (b) passes through the three points p, q and r, and another approximate expression having a characteristic curve (c) passes through the three points q, r and s. Either of these approximate expressions is selected depending on the detected steering torque, whereby the steering subsidiary command value corresponding to the steering torque is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for an electric power steering device.

[0002]

2. Description of the Related Art An electric power steering apparatus for a vehicle detects a steering torque and a vehicle speed generated in a steering shaft by operating a steering wheel, and calculates a steering assist command value based on the detection signal. The motor is driven in accordance with the steering assist command value to assist the steering force of the steering wheel. The calculation of the steering assist command value and the control of the motor based on the steering assist command value are performed by a microcontroller. Compilation
An electronic control circuit including the data is used.

Here, regarding the steering torque, there is a component corresponding to the road surface load generated by the steering and a component corresponding to the frictional force of the steering mechanism. For this reason, it has been proposed to calculate a steering assist command value by adding a control value corresponding to a road surface load determined based on a detected steering torque and a control value corresponding to a frictional force of a steering mechanism. I have.

In this configuration, a road surface load control value corresponding to the steering torque and a friction force control value corresponding to the steering torque are respectively determined in advance and stored in the memory, and are stored in the memory in accordance with the detected steering torque. The system is configured to read out necessary data and calculate a steering assist command value (see Japanese Patent Publication No. 5-10271).

[0005]

In the control means for calculating the steering assist command value as described above, the road surface load control value and the friction force control value are determined in advance according to the steering torque. Once determined, the steering assist command value changes only in accordance with the vehicle speed.

Accordingly, if a steering assist command value corresponding to a steering torque is preset for a plurality of vehicle speeds and stored in a memory, the steering assist command value can be immediately obtained from the detected steering torque and the vehicle speed. Can be.

FIG. 9 shows vehicle speeds V1 and V2 conventionally known.
, V3, the setting of a steering assist command value corresponding to the steering torque is described. For each vehicle speed, a steering assist command value I corresponding to the detected steering torque values T1, T2, T3, T4 is set. As shown in FIG. 9, for example, when the vehicle speed is V1, the steering assist command value I1 when the steering torque is T1, I2 when T2, I3 and T4 when T3.
When the steering torque is in the range of T1 and T2, the steering assist command value I1 is set. When the steering torque is in the range of T2 and T3, the steering assist command value is I2. When the steering torque is in the range of T3 and T4, the steering assist command is set. The memory capacity can be reduced by setting a constant steering assist command value I in steps, such as the value I3. However, if the steering assist command value I is set in a stepwise manner, the steering assist command value I does not change continuously according to changes in the vehicle speed or the steering torque, so that the steering assist force does not change smoothly, and the steering feeling is not changed. Has the disadvantage that it is not good.

As a countermeasure, the steering assist command value may be set as finely as possible in accordance with the steering torque and the vehicle speed. However, in this method, the required memory capacity is significantly increased, and the cost is increased. Become.

For this reason, for a representative vehicle speed, a steering assist command value corresponding to the steering torque is stored in the memory, and it is determined that the detected vehicle speed is intermediate between the representative vehicle speed stored in the memory. At this time, a steering assist command value corresponding to the steering torque for the representative vehicle speed before and after the detected vehicle speed is read from the storage means, and based on the difference between the detected vehicle speed and the vehicle speed correction coefficient, the detected vehicle speed and A method of calculating a steering assist command value corresponding to a steering torque has been proposed by the present applicant (Japanese Patent Application No. 6-316003).
issue).

However, for the above-described typical vehicle speed, even when the steering assist command value corresponding to the steering torque is stored in the memory, if the steering assist command value corresponding to the steering torque is finely set, the required memory capacity still increases. This results in increased costs. In addition, when the steering assist command value is changed, the data stored in the memory must be changed, which takes time and trouble. Another problem is that when calculating a steering assist command value corresponding to the steering torque, for example, when calculating with a finite word length of 8 bits, the lower digit (8 bits) of the calculation result (16 bits) is changed. The result is truncated and a quantization error based on the digital operation occurs. Such a quantization error is not desirable because it gives the driver a discontinuous steering feeling when performing gentle steering. An object of the present invention is to solve the above problems.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes a steering torque detecting means for detecting at least a steering torque generated in a steering shaft, and a steering assist command value based on the detected steering torque. A steering assist command value calculating means for calculating; and a motor current control means for controlling a motor current based on the calculated steering assist command value, and providing a steering assist force corresponding to the steering torque to the steering mechanism. In the control device of the electric power steering apparatus, the steering assist command value calculating means may include a higher order function formula that matches at least three points of a steering assist command value corresponding to a steering torque defined by a higher order function formula. The calculation means is based on a plurality of approximation function expressions that approximate the steering function. Characterized by calculating a steering assist command value. The plurality of approximate function expressions may be a plurality of quadratic function expressions.

The steering assist command value calculating means comprises a CPU for performing a numerical calculation based on the plurality of quadratic function expressions,
A calculating means for digitally calculating a steering assist command value sequentially based on a sample value of the steering torque sequentially detected at a predetermined time interval, while truncating a predetermined digit or less of the calculation result and outputting only the upper digit as a steering assist command value, It is preferable to add an adding means for adding the truncated error value of a predetermined digit or less in the calculation of the steering assist command value based on the sample value of the next steering torque. In this case, the calculation result of the steering assist command value calculation means is 16-bit data, and the digit to be truncated is the lower 8 bit data of the 16-bit data.

It is preferable that a low-pass filter is inserted on the output side of the steering assist command value calculating means. At this time,
The cut-off frequency of the low-pass filter is 1 / π or less of the Nyquist frequency of the control system.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features and embodiments of the present invention will be described below. The line (a) in FIG. 1 is a characteristic curve showing the relationship between the desired steering assist command value corresponding to the steering torque, and the relationship between the steering torque T and the steering assist command value In is higher (nth order).
Is defined as In = f (T) ⁿ . Therefore,
The steering assist command value In corresponding to the steering torque T can be obtained by performing a numerical operation based on the defined predetermined higher-order function formula In = f (T) ⁿ .

However, the CPU constituting the calculating means
Performing a numerical operation of the steering assist command value based on such a higher-order function expression is not realistic because it takes a long time to perform a complicated operation. For this reason, it is conceivable to perform a numerical operation using an approximate expression that approximates a higher-order function expression. When an approximation formula for interpolating these four points is determined, a fourth-order approximation formula is calculated. For example, when this approximation formula is calculated with a finite word length of 8 bits, the upper 8 bits are determined according to the magnitude of the coefficient of the approximation formula. However, the use of only the upper 8 bits increases the error due to lack of precision in the operation result due to the occurrence of a term without a significant digit or the increase in the number of multiplications. This can cause

Therefore, in the present invention, as shown in FIG. 1, four points (p, q,...) Are determined in advance from the steering assist command value corresponding to the steering torque defined by the higher-order function formula In = f (T) ⁿ .
r, s) are extracted, and two quadratic functional expressions interpolating three points (p, q, r) and (q, r, s) sharing two intermediate points (q, r) among them I decided to approximate.

That is, a quadratic function equation I1 for interpolating a point (p, q, r) and a quadratic function equation I1 for interpolating a point (q, r, s)
2 is defined as in the following equations (1) and (2).

I 1 = a 1 T ² + b 1 T + c (1) I 2 = a 2 T ² + b 2 T + c (2) And T: detected steering torques a1, a2, b1, b2, c: constants I1, I2: steering assist command value. In FIG. 1, line (a) is a higher-order function formula In = f representing a steering assist command value. (T) ⁿ indicates the characteristic curve, line (b) indicates the characteristic curve of the quadratic function equation I1 representing the steering assist command value, and line (c) indicates the characteristic curve of the quadratic function equation I2.

By approximating the higher-order function equation with the above two quadratic function equations, a steering assist command value corresponding to the steering torque can be easily obtained by calculation, and the quantization error is minimized. It is possible to do.

If one of the above-mentioned approximate expressions is selected according to the detected steering torque, and a steering assist command value corresponding to the detected steering torque is calculated based on the selected approximate expression, the calculation can be performed quickly and easily. It can be carried out.

When approximation is made using two quadratic function expressions for interpolating four points, the order of the function expression is low, so that the quantization error is reduced as compared with the case of the operation using the above-described quadratic function expression. be able to. In addition, in the case of approximation by two quadratic function expressions, since the approximation is made by one of the quadratic function expressions except for the transition point where one approximation expression shifts to the other approximation expression,
The change in the steering assist command value corresponding to the steering torque changes smoothly. As a result, the driver does not feel uncomfortable operating the steering wheel.

Further, in the present invention, a process described below is performed to reduce a quantization error in the calculation of the steering assist command value. That is, if the steering assist command value corresponding to the steering torque is calculated with a finite word length of 8 bits based on the quadratic function equation, the calculation result is output in 16 bits because it includes multiplication. However, since the motor drive circuit that controls the motor current by using the calculated steering assist command value as input, receives only 8-bit data, only the upper 8 bits of the calculation result output at 16 bits are output. The data is output to the motor drive circuit, and the lower 8 bits of data are discarded, which results in a quantization error.

Then, by adding the truncated lower 8-bit data to the steering assist command value calculated based on the steering torque detected in the next sampling period, the lower 8-bit data is truncated. It was made to reduce the conversion error.

FIG. 2 shows a quantization error reduction circuit represented by a transfer function. Reference numeral 101 denotes an operation for calculating a steering assist command value corresponding to a steering torque based on the above-described quadratic approximate expression (1). Element, addition element 102, operation element 103 for discarding lower 8-bit data of 16-bit data, 1
Reference numeral 04 denotes a storage element for temporarily storing the lower 8 bits of data cut off by the operation element 103, and reference numeral 105 denotes a gain adjustment element.

The operation of the quantization error reduction circuit will be described.
The detected steering torque T is input to the arithmetic element 101 as 8-bit data, and a steering assist command value is calculated based on the above-described approximate expression, and a 16-bit steering assist command value I1 is calculated.
Is output. The output data is input to the calculation element 103 via the addition element 102, the lower 8 bits of data are discarded, and the upper 8 bits of data are output as the steering assist command value I for control purposes. On the other hand, the truncated lower 8-bit data (quantization error) δ is temporarily stored in the storage element 104, the gain is adjusted by the gain adjustment element 105, and is read out in the next sampling period to be added to the addition element 1.
02 is output as data delayed by one sample period, and is added to the steering assist command value I1 calculated for the steering torque extracted in the next sampling period.

As described above, the lower-order 8 bits of data (quantization error) δ, which has been sequentially discarded, are added to the steering assist command value I1 based on the steering torque extracted in the next sampling period. It is possible to reduce a quantization error due to data truncation. The above description is of the quantization error reduction circuit based on the second-order approximation (1), but the same applies to the case based on the second-order approximation (2).

In the above-described quantization error reduction circuit shown in FIG. 2, the transfer characteristic from the occurrence of the quantization error to the output of the adder 102 has the characteristic of a high-pass filter, and shows the characteristic shown in FIG. Therefore, the low side is connected to the output side of the arithmetic circuit 103.
When a pass filter is inserted, as shown in FIG. 4, the gain becomes 1 or less at all frequencies, and the influence of the quantization error can be reduced at all frequencies.

Here, the quantization error is fed back by the reduction circuit shown in FIG. 2. However, the present invention is not limited to this, and any circuit having the characteristics of a high-pass filter can be used. Specifically, it is desirable to perform feedback so that the transfer characteristic becomes (1−Z ⁻¹ ) ⁿ . The higher the value n, the greater the effect of the high-pass filter effect. Also, the crossover of (1-Z ^-1 ) ⁿ
Since the frequency is 1 / π with respect to the Nyquist frequency,
It is desirable that the cutoff frequency of the low pass filter is 1 / π.

In the above description, it has been described that a low-pass filter is inserted at the output side of the quantization error reduction circuit. However, in an actual circuit, the motor that generates the steering assist force functions as a low-pass filter. Therefore, a low-pass filter is not required as a special circuit component. Further, the above-described quantization error reduction circuit does not include a reduction circuit formed of specific circuit elements in the control circuit, and is a function executed inside the CPU configuring the control circuit. .

The line (a) in FIG. 1 described above is a characteristic curve of a function formula In = f (T) ⁿ indicating a relationship between a desired steering assist command value corresponding to the steering torque. The function formula differs depending on the vehicle speed. Accordingly, a plurality of function formulas In = f (T) ⁿ indicating a desired steering assist command value corresponding to such a steering torque are set in accordance with the vehicle speed. Is set multiple times. By appropriately selecting an approximate expression according to the detected vehicle speed, and calculating a steering assist instruction value corresponding to the steering torque based on the selected approximate expression, it is possible to perform compensation of the steering assist instruction value based on the vehicle speed. You can.

[0031]

Embodiments of the present invention will be described below.
FIG. 5 is a diagram schematically illustrating the configuration of an electric power steering apparatus suitable for carrying out the present invention. The shaft 2 of the steering handle 1 is provided with a reduction gear 4, a universal joint 5a,
5b, which is connected to a tie rod 8 of a steered wheel via a pinion rack mechanism 7. The shaft 2 is provided with a torque sensor 3 for detecting the steering torque of the steering handle 1, and a motor 10 for assisting the steering force is connected to the shaft 2 via a clutch 9 and a reduction gear 4. I have.

An electronic control circuit 13 for controlling the power steering device is supplied from the battery 14 to an ignition key-1.
Power is supplied via 1. The electronic control circuit 13 calculates a steering assist command value based on the steering torque detected by the torque sensor 3 and the vehicle speed detected by the vehicle speed sensor 12, and based on the calculated steering assist command value, the motor 10. Control the current supplied to the

The clutch 9 is controlled by an electronic control circuit 13. The clutch 9 is engaged in a normal operation state, and is disconnected when the electronic control circuit 13 determines that the power steering device has failed and when the power is off.

FIG. 6 is a block diagram of the electronic control circuit 13. In this embodiment, the electronic control circuit 13 is mainly composed of CP
U, but here the functions executed by the program inside the CPU are shown. For example, the phase compensator 21 does not indicate the phase compensator 21 as independent hardware, but indicates a phase compensation function executed by the CPU.

The function and operation of the electronic control circuit 13 will be described below. The steering torque signal input from the torque sensor 3 is phase-compensated by the phase compensator 21 to enhance the stability of the steering system, and is input to the steering assist command value calculator 22. The vehicle speed detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 22.

The steering assist command value calculator 22 determines a steering assist command value I, which is a control target value of the current supplied to the motor 10, based on the input torque signal and vehicle speed signal.

The circuit composed of the comparator 23, the differential compensator 24, the proportional calculator 25, the integral calculator 26 and the adder 27 ensures that the actual motor current value i matches the steering assist command value I. This is a circuit for performing feedback control.

The proportional calculator 25 outputs a proportional value proportional to the difference between the steering assist command value I and the actual motor current value i. Further, the output signal of the proportional calculator 25 is integrated in the integrating calculator 26 in order to improve the characteristics of the feedback system, and the proportional value of the integrated value of the difference is output.

The differential compensator 24 increases the response speed of the motor current value i actually flowing to the motor to the steering assist command value I calculated by the steering assist command value calculator 22.
A differential value of the steering assist command value I is output.

The differential value of the steering assist command value I output from the differential compensator 24, a proportional value proportional to the difference between the steering assist command value output from the proportional calculator 25 and the actual motor current value, and The integration value output from the integration calculator 26 is added in the adder 27, and the current control value E as the calculation result is output to the motor drive circuit 41 as a motor drive signal.

FIG. 7 shows an example of the configuration of the motor drive circuit 41. The motor drive circuit 41 converts the current control value E input from the adder 27 into a PWM signal and a current direction signal, and converts the current control value E into a PWM signal and a current direction signal.
It comprises an FET gate drive circuit 45 for opening and closing the gates of T1 to FET4. The boost power supply 46 is connected to the FET1
, And a power source for driving the high side of FET2.

The PWM signal (pulse width modulation signal) is a signal for driving the gates of the H bridge-connected FETs (field effect transistors) switching elements FET1 and FET2, and the current control value E calculated by the adder 27. Determines the duty ratio of the PWM signal (the time ratio for turning on / off the gate of the FET).

The current direction signal is a signal indicating the direction of the current supplied to the motor, and is determined by the sign (positive or negative) of the current control value E calculated by the adder 27.

FET1 and FET2 are switching elements whose gates are turned ON / OFF based on the duty ratio of the PWM signal, and are switching elements for controlling the magnitude of the current flowing to the motor. . Also, FET3
And the gate of the FET 4 is turned ON or OFF based on the above-mentioned current direction signal (when one is ON, the other is OF).
F), which is a switching element for switching the direction of the current flowing through the motor, that is, the direction of rotation of the motor.

When the FET 4 is in a conductive state, a current flows through the FET 1, the motor 10, the FET 4, and the resistor R1, and a forward current flows through the motor 10. FET3
Is in the conductive state, the current flows through the FET2 and the motor 1.
0, a current flows through the FET3 and the resistor R2, and the motor 10
Current flows in the negative direction.

The motor current detection circuit 42 detects the magnitude of the positive current based on the voltage drop across the resistor R1, and detects the negative current based on the voltage drop across the resistor R2. Detect size. The detected actual motor current value i is fed back to the comparator 23 and input (see FIG. 6).

Next, the steering assist command value calculator 2 of the present invention
2 will be described.

As described above, according to the present invention, a higher-order function formula I defining a steering assist command value corresponding to a steering torque is provided.
n = f (T) ⁿ is approximated by the above equations (1) and (2), and the steering assist command value is calculated by the equations (1) and (2).
Hereinafter, the calculation process executed by the steering assist command value calculator 22 will be described with reference to a flowchart shown in FIG.

First, the steering torque is sampled to detect the steering torque T (step P1). This can be achieved by extracting the output from the torque sensor 3 at predetermined time intervals. Next, it is determined whether or not the detected steering torque T is larger than a predetermined value Tc set in advance (step P2). This is the higher-order function I described above.
n = f (T) In ^order to determine which of the equations (1) and (2) approximated to ⁿ should be used to calculate the steering assist command value corresponding to the steering torque, the predetermined value Tc is For example, it is the value of the steering torque at the point (r) in FIG.

If it is determined in step P2 that T> Tc, the process proceeds to steps P3 and P4. Here, the steering assist command value I1 is calculated by the equation (1). However, since the equation (1) includes a term of the square of T, the steering assist command value I1 is calculated in two steps to facilitate the calculation. ^{That, I1 = a1 T 2 + b1} T + c ············· (1) can be rewritten as follows.

I1 = (a1 × T + b1) × T + c (3) Therefore, in the following calculation, (a1 ×
T + b1) is calculated to determine the intermediate value I0, and (I0.times.T + c) is calculated as the second calculation.

First, the first calculation is performed. For the coefficient a1,
The steering torque T is multiplied by the value (T + δ0) obtained by adding the error δ0 of the lower eight bits rounded down in the calculation based on the previous sample (T + δ0), and the upper eight bits Q [a1 ×
(T + δ0)] and the coefficient b1. That is, ｛Q [a
1 × (T + δ0)] + b1} is calculated as an intermediate value I0. Also, the lower 8 bits R [a1 × (T + δ0
)] Is stored in the memory as a new lower 8 bit error δ0, and is added in the next sample calculation (step P3).

Here, Q is a symbol meaning upper 8 bits, Q [-] means upper 8 bits data, R is a symbol meaning lower 8 bits, and R [-] is lower 8 bits data. (Step P3).

Next, the operation proceeds to the second calculation. A value obtained by adding the steering torque T and the error δ1 of the lower 8 bits rounded down in the calculation based on the previous sample to the intermediate value I0 calculated previously (T
+ [Delta] 1), and the coefficient c1 is added to the upper eight bits Q [I0 * (T + [delta] 1)] to calculate the steering assist command value I1. That is, ｛Q [I0 × (T
+ Δ1)] + c1} is calculated. In addition, the lower 8
The bit R [I0.times. (T + .delta.1)] is stored in the memory as a new lower 8 bit error .delta.1, and is added in the next sample operation (step P4).

If it is determined in step P2 that T.ltoreq.Tc, the process proceeds to steps P5 and P6, and the same calculation as in steps P3 and P4 is performed. First, in the first calculation, the coefficient a2 is multiplied by a value (T + δ0) obtained by adding the steering torque T and the error δ0 of the lower 8 bits rounded down in the calculation based on the previous sample (T2 × (T + δ0)). Bit Q [a2 ×
(T + δ0)] and the coefficient b2, and ｛Q [a2 × (T +
.delta.0)] + b2} is calculated and set as an intermediate value I0. Also,
The truncated lower 8 bits R [a2.times. (T + .delta.0)] are stored in the memory as a new lower 8 bit error .delta.0, and added in the next sample operation (step P5).

Next, the process proceeds to the second calculation, in which the steering torque T and the error δ1 of the lower 8 bits rounded down in the calculation based on the previous sample are added to the previously calculated intermediate value I0 (T
+ [Delta] 1) [I0 * (T + [delta] 1)], and the coefficient c2 is added to the upper 8 bits Q [I0 * (T + [delta] 1)] to calculate the steering assist command value I1. That is, ｛Q [I0 × (T
+ Δ1)] + c2}. In addition, the lower 8
The bit R [I0.times. (T + .delta.1)] is stored in the memory as a new lower 8 bit error .delta.1, and is added in the next sample operation (step P6).

Next, the vehicle speed interpolation calculation (step P7) is performed to determine and output the steering assist command value I (step P7).
8) The process returns to step P1 for calculation based on the next steering torque sample.

Here, the vehicle speed interpolation calculation will be described. As described above with reference to FIG. 9, the relationship between the steering assist command value corresponding to the steering torque changes according to the vehicle speed. Therefore, since a plurality of approximate expressions of the function formula for determining the steering assist command value are also set according to the vehicle speed, the above-described calculation is performed by appropriately selecting an approximate expression according to the detected vehicle speed. By performing the correction corresponding to the intermediate vehicle speed,
A more appropriate steering assist command value can be calculated. Such a vehicle speed interpolation calculation has already been proposed by the present applicant (Japanese Patent Application No. 6-316003), and is not the purpose of the present application, so a detailed description thereof will be omitted here.

In the embodiment described above, the electronic control circuit is constituted by an 8-bit CPU, and in calculating the steering assist command value, the upper 8 bits of the 16-bit data obtained in the calculation process are used for the steering assist command value. It has been described that the data is output as data and the lower 8 bits are added to the next operation as an error. However, this is an explanation assuming that the electronic control circuit is constituted by an 8-bit CPU. Even when the electronic control circuit is constituted by a CPU other than the 8-bit CPU, the upper bits are similarly set to the steering assist command value data. When output as negative data, the lower bit data becomes an error. It is needless to say that the processing method of the present invention in which such an error is added to the next operation can be applied to data processing by a CPU other than 8-bit as a method of reducing a quantization error based on digital operation. Absent.

[0060]

As described above, in the control device of the electric power steering apparatus according to the present invention, the steering assist command value corresponding to the steering torque is defined by a predetermined higher-order function formula.
Since the steering assist command value corresponding to the detected value of the steering torque is calculated and determined based on the approximation formula approximating the higher-order function formula, the steering assist command value corresponding to the steering torque is stored in the memory. As in the above, an appropriate steering assist command value corresponding to the steering torque can be obtained without requiring a remarkably large capacity memory, and an electric power steering apparatus having a smooth steering feeling can be provided.

When the steering assist command value corresponding to the steering torque is calculated, the lower digits of the calculation result are truncated when the calculation is performed with a finite word length, and a quantization error based on digital calculation is generated. According to this, such an error is added in the next calculation process, so that the quantization error can be reduced, and in particular, the driver does not give a discontinuous steering feeling to the driver when performing gentle steering, and the An electric power steering apparatus having a steering feeling can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a characteristic curve when a desired steering assist command value corresponding to a steering torque is expressed by a higher-order functional expression, and setting of an approximate expression according to the present invention.

FIG. 2 is a circuit diagram of a quantization error reduction circuit represented by a transfer function.

FIG. 3 is a diagram illustrating transfer characteristics of a quantization error reduction circuit.

FIG. 4 is a diagram for explaining transfer characteristics when a low-pass filter is inserted on the output side of the quantization error reduction circuit.

FIG. 5 is a diagram schematically illustrating the configuration of an electric power steering device.

FIG. 6 is a block diagram of an electronic control circuit according to the embodiment of the present invention.

FIG. 7 is a circuit block diagram showing a configuration of a motor drive circuit.

FIG. 8 is a flowchart for explaining a process for calculating a steering assist command value.

FIG. 9 is a view for explaining setting of a steering assist command value corresponding to a conventional steering torque.

[Explanation of symbols]

 Reference Signs List 3 Torque sensor 10 Motor 12 Vehicle speed sensor 13 Electronic control circuit 21 Phase compensator 22 Steering assist command calculator 23 Comparator 24 Differential compensator 25 Proportional calculator 26 Integral calculator 27 Adder 41 Motor drive circuit 42 Mo -Data current detection circuit 44 converter 45 FET gate drive circuit

Claims (6)

[Claims] 1. A steering torque detecting means for detecting at least a steering torque generated in a steering shaft; a steering assist command value calculating means for calculating a steering assist command value based on the detected steering torque; A controller for an electric power steering device, comprising: motor current control means for controlling a motor current based on an auxiliary command value, wherein the control device provides a steering assisting force according to a steering torque to a steering mechanism. The calculating means is constituted by calculating means based on a plurality of approximate function formulas that approximate the higher-order function formula that matches at least three points of the steering assist command value corresponding to the steering torque defined by the higher-order function formula. An electric power, wherein a steering assist command value corresponding to the detected value of the steering torque is calculated by calculation means based on the approximate function formula. The control device of tearing devices. 2. The control device for an electric power steering apparatus according to claim 1, wherein the plurality of approximate function expressions are a plurality of quadratic function expressions. 3. The steering assist command value calculating means includes a CPU for performing a numerical operation based on the plurality of quadratic function expressions, and sequentially performs steering assist based on sample values of steering torque sequentially detected at predetermined time intervals. A calculation means for digitally calculating a command value, wherein a predetermined digit or less of a calculation result is truncated, and only the upper digit is output as a steering assist command value, and an error value of the predetermined digit or less is based on a sample value of the next steering torque. 2. The control device for an electric power steering apparatus according to claim 1, further comprising an adding means for adding in the calculation of the steering assist command value. 4. The operation result of the steering assist command value calculating means is 16-bit data, and the digit to be discarded is the lower 8 bit data of the 16-bit data. Control device for electric power steering device. 5. The control device for an electric power steering apparatus according to claim 3, wherein a low-pass filter is inserted on an output side of the steering assist command value calculating means. 6. The cut-off frequency of the low-pass filter is:
6. The control apparatus for an electric power steering apparatus according to claim 5, wherein the control power is not more than 1 / π of the Nyquist frequency of the control system.